It is well known in the art of downhole remedial cutting tools to utilize the principle of pumping drilling fluid through a nozzle or restriction near the lower end of the drill string to drop the pressure in the well bore annulus around the tool body by a calculated amount. This creates a pressure differential between the high pressure inside the tool and the now lower pressure in the well bore annulus. This pressure differential is used to drive a piston, for example, to extend hinged cutter arms. When the cutter arms are forced by the piston into the extended cutting position, the drill string is rotated and the cutters mill up steel casing, rock formation or other downhole equipment. The cuttings from the milling operation ofttimes are very difficult to remove from the well bore to the surface. This is especially true in high angle holes. The steel cuttings and other debris tend to pack-off on the lower side of the essentially horizontal hole. It is, therefore, imperative that high fluid volumes and velocities be used to efficiently clear the hole of cuttings as the milling tool is prone to getting stuck in the borehole. This is especially true if the fluid flow is stopped or greatly reduced.
Pumping high volumes of drilling fluid while "tripping" the drill string out of the hole or while rotating and moving the drill pipe up and down inside casing with the tool arms closed is generally desirable but is not possible with equipment now available.
The hydraulically activated cutter arms tend to jam if the acuator nozzle plugs and the float valve traps pressure between the float valve and the nozzle.
Although present day equipment for remedial borehole work do a very credible job, there are circumstances that cause acute problems such as stuck drill string with associated "fishing" jobs, lost equipment in the hole and damaged casing to list a few. All of the above problems are very costly, dangerous and time consuming, especially in the offshore domains such as the North Sea, the Arctic and other areas where the operating costs can be up to $60,000 per day.
This invention minimizes the aforementioned risks usually associated with the use of present day hydraulically expandable remedial oil field tools.